Force Merge API

Force merge Request

A ForceMergeRequest can be applied to one or more indices, or even on _all the indices:

ForceMergeRequest request = new ForceMergeRequest("index1"); 
ForceMergeRequest requestMultiple = new ForceMergeRequest("index1", "index2"); 
ForceMergeRequest requestAll = new ForceMergeRequest(); 

Force merge one index

Force merge multiple indices

Force merge all the indices

Optional arguments

request.indicesOptions(IndicesOptions.lenientExpandOpen()); 

Setting IndicesOptions controls how unavailable indices are resolved and how wildcard expressions are expanded

request.maxNumSegments(1); 

Set max_num_segments to control the number of segments to merge down to.

request.onlyExpungeDeletes(true); 

Set the only_expunge_deletes flag to true

request.flush(true); 

Set the flush flag to true

Synchronous Execution

When executing a ForceMergeRequest in the following manner, the client waits for the ForceMergeResponse to be returned before continuing with code execution:

ForceMergeResponse forceMergeResponse = client.indices().forcemerge(request, RequestOptions.DEFAULT);

Synchronous calls may throw an IOException in case of either failing to parse the REST response in the high-level REST client, the request times out or similar cases where there is no response coming back from the server.

In cases where the server returns a 4xx or 5xx error code, the high-level client tries to parse the response body error details instead and then throws a generic ElasticsearchException and adds the original ResponseException as a suppressed exception to it.

Asynchronous Execution

Executing a ForceMergeRequest can also be done in an asynchronous fashion so that the client can return directly. Users need to specify how the response or potential failures will be handled by passing the request and a listener to the asynchronous force-merge method:

client.indices().forcemergeAsync(request, RequestOptions.DEFAULT, listener); 

The ForceMergeRequest to execute and the ActionListener to use when the execution completes

The asynchronous method does not block and returns immediately. Once it is completed the ActionListener is called back using the onResponse method if the execution successfully completed or using the onFailure method if it failed. Failure scenarios and expected exceptions are the same as in the synchronous execution case.

A typical listener for force-merge looks like:

ActionListener<ForceMergeResponse> listener = new ActionListener<ForceMergeResponse>() {
    @Override
    public void onResponse(ForceMergeResponse forceMergeResponse) {
        
    }

    @Override
    public void onFailure(Exception e) {
        
    }
};

Called when the execution is successfully completed.

Called when the whole ForceMergeRequest fails.

Force Merge Response

The returned ForceMergeResponse allows to retrieve information about the executed operation as follows:

int totalShards = forceMergeResponse.getTotalShards(); 
int successfulShards = forceMergeResponse.getSuccessfulShards(); 
int failedShards = forceMergeResponse.getFailedShards(); 
DefaultShardOperationFailedException[] failures = forceMergeResponse.getShardFailures(); 

Total number of shards hit by the force merge request

Number of shards where the force merge has succeeded

Number of shards where the force merge has failed

A list of failures if the operation failed on one or more shards

By default, if the indices were not found, an ElasticsearchException will be thrown:

try {
    ForceMergeRequest request = new ForceMergeRequest("does_not_exist");
    client.indices().forcemerge(request, RequestOptions.DEFAULT);
} catch (ElasticsearchException exception) {
    if (exception.status() == RestStatus.NOT_FOUND) {
        
    }
}

Do something if the indices to be force merged were not found